*clipboard*

This variable holds the stack of lisp clipboard values. The value is
a list where each element is an item in the Lisp clipboard stack, with
the first item in the list being the topmost (most recent) item on the
stack. Each item is a cons whose car is the actual clipboard value
and whose cdr is the keyword symbol naming its OS clipboard
format. Some of the clipboard values near the top may be the symbol
:needs-conversion; this indicates a value that was
copied in another application and has not yet been pasted in Lisp ---
Lisp avoids actually reading the value from the OS clipboard until
needed, for efficiency.